Paper of improved dry strength and method of making same



United States Patent PAPER OF IMPROVED DRY STRENGTH AND METHOD OF MAKING SAME Lucius H. Wilson, Riverside, Walter M. Thomas, Noroton Heights, and John I. Padbury, Old Greenwich, Conn., assignors to American Cyanamid Company, New York, N.Y., a corporation of Maine No Drawing. Application February 25, 1954 Serial No. 412,648

12 Claims. (Cl. 162-164) The present invention relates to cellulosic webs of improved dry strength. The invention relates to such webs and particularly to paper comprising cellulosic fibers having uniformly adsorbed thereon a small but efiective amount of a normally water-soluble linear polymer containing quaternary ammonium groups as agent imparting the dry strength referred to. The invention includes paper, paper board, and other webs composed of fibers carrying in addition to the dry strength agent rosin and other sizing agents, hydrophobic organic impregnating agents, wet strength agents, fillers, dyes, and pigments. The invention further includes methods for manufacturing various types of cellulosic webs described.

The novel strengthened cellulosic webs of the present invention ,are suitable for special use as bank note, bond, ledger and book paper; map, blueprint and graph paper; newsprint paper; wrapping paper and bag paper; paper toweling; saturating papers; cardboard, hardboard, and insulating board; other formed, pressed webs; and shaped articles of the type formed from papier-mach.

By dry strength is meant the strength of the cellulosic web in its normally dry condition, and paper which has a dry strength about in excess of its normal strength as the result of resin treatment is generally regarded as possessinga materially improved dry strength.

The invention is based chiefly upon our discovery that cellulosic webs composed of cellulosic fibers having uniformly adsorbed thereon a small amount of a normally water-soluble high molecular weight linear chain polymer carrying quaternary ammonium groups as more particularly hereinafter described possess materially increased dry strength. That is, we have found that when cellulosic fibers are slurried with an aqueous suspension containing a polymer of the type mentioned, the polymer is rapidly adsorbed by the fibers and that when the thus treated fibers thus carrying a uniformly adsorbed amount of the polymer are made into a web and the web is dried, the resulting web possesses materially greater dry strength than that possessed by corresponding webs composed of cellulosic fibers having adsorbed thereon none of the polymers referred to.

The strengthening agents employed in the present invention are synthetic, hydrophilic, cationic linear chain polymers or macromolecules containing quaternary ammonium groups. The chains may be polyalkane chains containing only carbon atoms, polyazaalkane chains containing carbon and nitrogen atoms, polyoxaalkane chains containing carbon and oxygen atoms, or polythiaalkane chains containing carbon and sulfur atoms. Moreover, chains may be composed of a variety of atoms including carbon, nitrogen, sulfur, and oxygen atoms or may be 2,884,057 Patented Apr. 28, 1959 ice composed wholly of carbon atoms. Further, the chains may carry a variety of substituents, as will be more fully disclosed. The strengthening agents themselves are cationic polyelectrolytes which have the capacity of substantively depositing themselves on cellulosic fibers in aqueous suspension and, when so deposited, increase the dry strength of paper made therefrom. The deposition is irreversible in that the resin is not removed during the steps to which the fibers are normally subsequently subjected in their manufacture into paper.

It is a feature of the invention that useful results are obtained in the case of inherently water-soluble polymers when each polymeric macromolecule contains a surprisingly small proportion of quaternary ammonium group, proportions being in the range of one such group for every 1,000 linear chain atoms. As a result, it appears that in such cases it is sufiicient if each macromolecule contains even one quaternary ammonium group. On the other hand, distinct strengthening effects have been observed when there are present as many as 500 quaternary ammonium groups for each 1,000 atoms of the chain.

The strengthening agents are normally water-soluble; that is, they are water-soluble in the form employed. When adsorbed on cellulose fibers, however, they appear to become insoluble and are not removed to any significant extent by ordinary washing.

In numerous instances a significant strengthening effect is noted when the fibers have adsorbed thereon as little as 0.01%, based on their dry weight, of the strengthening agent and may carry as much as 5%10% or more. A near maximum improvement in strength takes place when the fibers carry roughly l%-3% of the material, larger amounts acting to improve the dry strength still further, but not in proportion to the amount added.

The mechanism by which these agents act is not known, but evidently they strengthen or supplement the normal gelatinous fiber-to-fiber bonding or cementation which takes place when the fibers are sheeted from aqueous suspension and the sheets thus formed are dried.

From the foregoing it will be seen that the strengthened cellulosic webs of the present invention consist essentially of interfelted cellulosic fibers having uniformly adsorbed thereon from 0.01% to 10%, based on their Weight, and preferably about 1% to 3% of a long chain normally water-soluble linear polymer carrying qua- .ternary ammonium groups. In addition, the web may contain a normally effective amount of any of the common sizing materials, including rosin size, cationic size, or wax size, and from 2% to as much as 30% of the usual fillers and pigments, including alkaline fillers such as calcium carbonate.

The evidence is that any type of cellulose fiber is benefited by the process of the present invention, and that the greatest percentile increases in dry strength result when the polymers are applied to weak fibers, that is, to lightly beaten fibers.

The preferred strengthened papers of the present invention possess the following characteristics. The basis of comparison in each instance is corresponding paper which contains no strengthening agent.

1) The papers of the present invention, if made on the acid side, retain their dry strength although subsequently exposed to alkaline conditions, and conversely, if made under alkaline conditions, they retain their dry strength although exposed to acid conditions. As a reaesaoev "sult, they are not significantly affected by the presence of normally alkaline fillers such as calcium carbonate and may be used for packaging normally acidic or alkaline materials such as acid fertilizers and alkaline cements.

(2) The papers of the present invention possess greatly increased dry strength, increases of up to 30%-50% in dry tensile strength being common.

(3) The papers need not have any metal content or content of combined formaldehyde, and thus are advantageously used for analytical laboratory filtration paper and as photographic paper.

(4) The papers possess substantially the same caliper, porosity, density, odor, color, feel and printing qualities as ordinary paper.

(5) The papers, unless otherwise desired, possess low wet strength. As a result, unless intentionally given high wet strength properties, the papers of the present invention are readily repulped by ordinary beating without need for special equipment.

The process for manufacturing strengthened paper according to the present invention comprises three principal steps; forming an aqueous suspension of cellulosic fibers; adding an aqueous solution of the strengthening agent thereto, thereby adsorbing the strengthening agent on the fibers; and sheeting and drying the fibers to form the desired cellulosic web.

The first step of forming an aqueous suspension of cellulosic fibers is performed by any conventional method. It usually involves beating and refining the fibers, the suspension thereafter being adjusted to a convenient consistency between about 0.1% and 36%. However, the primary effect of beating is to increase the bonding capacity of the cellulose fibers. Hence, in those instances when paper of ordinary strength is satisfactory, addition of the dry strength polymer permits a sharp curtailment in the duration of beating which would otherwise be necessary for this purpose.

The second step is performed 'by adding an aqueous solution of the strengthening agent to the cellulosic suspension and rapidly and uniformly distributing the solution therethrough so as to minimize uneven adsorption of the agent by the fibers. The step is most conveniently performed by adding the solution to a turbulent stream of the suspension at the headbox or other point near the webforming wire. It is practical, however, to incorporate the strengthening agent in the beater or even in a stock storage tank, in the latter event the stock being most advantageously agitated during the addition and the solution being added in rather dilute form. The pH of the suspension may be any value between 3 and 11, but in most r instances slightly better results are obtained in the range of 4.5-9.0.

Manipulatively, the third step is performed in conventional manner, but it is a feature of the present invention that agents which are free from combined formaldehyde develop substantially their maximum strengthening effect when the paper during its entire manufacture is maintained at a low temperature and are not significantly affected by exposures to elevated temperature for such time as are common in the manufacture of ordinary paper. As a result, no additional heat is required, and in certain instances heat may be saved, while producing a paper of low or negligible wet strength. On the other hand, when the paper is subjected to normal drying conditions, for example 200250 F. for /2 to 3 minutes and the resin contains combined formaldehyde, the dry strength increases only slightly over corresponding resin-treated paper which has not been heated whereas the wet strength values obtained rise markedly. As a result, when paper is produced with the broke recovery problem in view a minimum effective drying temperature will be employed or a resin will be selected which contains no combined formaldehyde and a formaldehyde-containing resin will be used at a higher drying temperature when the paper is expected to exhibit substantial wet strength. There is no sharp line of division between these two ranges, the wet strength rising steadily as the drying temperature is increased while the dry strength values rise similarly but at a much slower rate.

It is possible to incorporate the method just described in many of the commercially important processes for the manufacture of sized paper.

For example, before addition of the strengthening agent the fibers may be sized in normal manner by the addition of rosin size and alum, or. by the addition of wax size and alum, or by the addition of the substantively adsorbed sizing agents of Argentine Patent Nos. 86,126 and 86,826. Argentine Patent No. 86,126 discloses the manufacture of alkali-resistant sized paper by beater addition of the cationic condensation product of 1-2 'mols of epichlorohydrin with one mol of one or more aliphatic amines containing at least 16 carbon atoms. Argentine Patent No. 86,826 discloses a similar paper manufacturing method wherein the fibers are sized by addition of a polyalkylenepolyamine-fatty acid condensate in the form of an aqueous dispersion of a water-soluble salt thereof. The strengthening agents of the present invention are not adversely affected by the small amount of residual alum normally remaining after such sizing operations.

Alternatively, a colloidal cationic amine-aldehyde wet strength resin may be added such as that shown in U.S. Patent No. 2,345,543, preferably before or after the addition of the dry strength resin. 7

Alternatively still, impregnated paper may be formed by adding subsequent to incorporation of the dry strength polymer a hydrophobic organic impregnating agent in dispersed form as disclosed in U.S. Patent No. 2,563,897, the dry strength resin acting in manner similar to the melamine-aldehyde there employed to flocculate and irreversibly deposit on the fibers the dispersed impregnating agent.

The manufacture of rosin-sized paper containing an acid-sensitive inorganic filler such as calcium carbonate in the past has been regarded as impractical, the alum normally added to precipitate rosin sizing changing the pH of the suspension to the acid side resulting in foam from decomposition of any calcium carbonate present. On the other hand, if addition of the calcium carbonate is deferred until the rosin size is deposited on the fibers, the calcium carbonate raises the pH of the suspension causing the rosin to be desorbed by the fibers.

A recent development of the paper art is the series of cationic alkali resistance sizes disclosed in the Argentine patents referred to. The dry strength resins of the present invention are compatible therewith and paper of improved dry strength may be readily manufactured by first adding the cationic alkali resistance size as described in said patents, then adding one of the dry strength resins of the present invention, and finally adding the calcium carbonate.

Strengthening agents suitable for use in the present invention may be made by three principal methods.

According to one method, a preformed polyazaalkane is employed containing tertiary nitrogen groups such as polymerized N-methyl-ethylenimine having a viscosity of about 60120 seconds as measured by the fall time of a 3 mm. steel ball through 20 mm. of a 50% aqueous solution of the polymer at 20 C. This polymer may be quaternized by the addition of a small amount of an alkyl or aryl halide. The product is a heterogeneous chain composed of recurring alkylene groups between recurring quaternized N atoms. If desired, the two steps may be combined by coreacting a compound-containing two tertiary amino groups such as tetrarnethyl p-phenylenediamine with ethylene dibromide. The resulting polymers contain linkage of the type wherein X represents halogen or hydroxyl, Y represents alkyl or aryl, and Z represents alkylene or arylene groups.

According to a second method, a linear polymer is employed which carries halogenated substituents, quaternization being efiected by addition of a tertiary amine. Thus, for example, polymerized allyl chloroacetate may be quaternized with pyridine, polymerized p-(chloromethyl) styrene may be quaternized by reaction with triethylamine, and the quaternary ammonium compound formed by reacting N-(dimethylamino)propionamide may be reacted with polymerized N-hydroxymethylacrylamide. The resulting polymers contain linkages of the type wherein Z represents essentially inert groups such as arylene, alkylene, -CONH(CH COOCH CH CHCOOCH and CONHCH NHCOCH CH and X and Y as shown above. Moreover, Z and N may be present in one grouping, as in the case of a heterocyclic ring, for example, pyridine.

The third method is based upon copolymerization of a monomeric or low molecular weight quaternary ammonium compound with one or more monomers or low molecular Weight compounds copolymerizable therewith. Thus, for example, an t n-unsaturated quaternary ammonium compound such as trimethyl vinylbenzyl ammonium chloride may be copolymerized with an cap-unsaturated hydrocarbon, amine, amide, ester, or mixtures thereof such as styrene, acrylamide, ethyl acrylates, etc. to give a linear chain carbon polymer carrying a desirable proportion of quaternary ammonium groups. Other polymerizable quaternary ammonium compounds may be prepared from dimethylaminopropyl-acrylamide and benzyl chloride; from ethyl diethylamino-acrylate and benzyl bromide; and from methylene bisacrylamide reacted with diisopropylamine followed by quaternization with butyl bromide.

When adjusted to pH 7 the polymers are stable and may be stored for at least several months before use. They are prepared for addition to the pulp suspension by dilution with water to a convenient solids content normally 5-10% and the pH of the resulting solutions may be maintained between 4 and 9 for several hours Without harm.

Very satisfactory results have been obtained in the case of polymers having molecular weights (calculated from viscosity measurements) of 50,000, 100,000, and 150,000, practically the same dry strength being imparted in each case, and there, therefore, does' not appear to be any theoretical maximum to the molecular weight which the polymer may attain. It is to be expected, however, that the strengthening efiect will fall considerably when the low molecular weight stage is approached too closely, and from experience with similar polymers the evidence is that the reaction should be controlled by known means so that a molecular weight of at least about 10,000-25,000 is obtained to make the polymer practically useful.

At the other extreme, with increase in molecular weight the polymers become more and more viscous, and a practical maximum is set when the polymer is so viscous that 2% aqueous solutions thereof are beyond pumpable viscosity. Generally, polymers of a molecular weight of 200,000 are satisfactorily fluid and give substantially the best results of their respective types.

The number of quaternary ammonium groups present should be at least one, on the average, for every macromolecule present, and for best results because of the heterogeneity of the reactions employed it is preferred to provide considerably more. In general, therefore, at least about one quaternary ammonium group is present for every 1,000 atoms forming the chain, and no more than about 50 such groups calculated on the same basis is required to provide satisfactory dry strength.

It is necessary, however, that the polymers be watersoluble or water-dispersible in the sense that when mixed with water they form a completely homogeneous and usually clear or colloidal cationic dispersion therewith, audit is possible to form polymers containing a large proportion of hydrophobic or insolubilizing groups.

Quaternary ammonium groups have a solubilizing action and hence, an additional proportion of these groups may be present over the amounts recited above in order to confer on them a solubility which otherwise would be lacking. Thus, when a monomeric a,,BUnSatl1- rated quaternary ammonium compound is copolymerized with styrene or an acrylate ester, the phenyl or ester groups in the resulting polymer exert their normal strongly hydrophobic influence. In such instances an excess of the quaternary ammonium compound is necessary to form a water-soluble polymer. On the other hand, when a polymer is formed by copolymerizing acrylamide with an n p-unsaturated quaternary ammonium compound, the amide groups in the resulting polymer act as solubilizing groups permitting the use of a comparatively low amount of the quaternary ammonium compound for formation of a water-soluble or waterdispersible polymer. In general, hydrocarbons and ester groups act in hydrophobic manner when formed into linear polymers and require the presence of a comparatively large proportion of quaternary ammonium groups whereas amine, hydroxy, polyglycol and amide groups are hydrophilic when formed into linear polymers and require minimum amotmts of the quaternary ammonium compound for development of water-soluble polymers. A similar relationship holds with regard to the structure of the chains, fewer quaternary ammonium groups being required in the case of polyazaalkyl chains than in the case of straight chain carbon or polyalkane chains because of the solubilizing eifect of the nitrogen atoms therein.

The minimum efiective amount of the quaternary ammonium compound necessary in each instance is thus a function of the type of linear chain employed and the number and type of substituent groups attached thereto. As a result, the proportion of quaternary ammonium groups which should be present can be most conveniently determined by actual trial, a resin being formed first employing a comparatively small amount of the quaternary ammonium monomer and, if the resulting resin proves insoluble, increasing the proportion of the quaternary ammonium monomer until a water-soluble resin is obtained.

The dry strength resins prepared by copolymerization of monomers which contain only such groups as ester, carboxylic acid, alkoxy, aryloxy, and unsubstituted or hydrocarbon substituted amide and amine groups yield paper which has negligible wet strength. Such polymers are essentially chemically inert under the conditions employed and, therefore, form bonds with the cellulose which are loosened by the presence of water.

It is readily feasible to modify the polymers described so as to make them chemically reactive whereby on heating they will form a water-insoluble composition giving Wet strength as well as dry strength. Most simply, this is done by ensuring that the polymer, before addition to the fibrous cellulose suspension, contains combined formaldehyde. Thus, a very minor amount of an a e-quaternary ammonium compound may be copolymerized with a major amount of an B-unsaturated N-methylol amide such as N-hydroxymethyl-acrylamide. The re sulting polymer is employed in the same manner as the polymers described above, except that the paper during drying thereafter is heated at about 200-260 F. for /2 to minutes. A paper of much improved wet strength is obtained which also exhibits improved dry strength.

Adsorption of the dry strength resin by the fibers takes place practically completely when a small amount, e.g. 1%3% of the dry strength resin is added, based on the weight of the fibers. Adsorption values fall off as larger amounts become present due to decreased receptivity of the fibers therefor.

The invention will be more particularly illustrated by the examples which follow, which represent specific embodiments of the present invention and which are not to be construed as limitations thereof.

Example 1 One method of forming a long carbon chain polymer suitable for quaternization to form a dry strength resin is illustrated by the following.

5.5 gm. of a polystyrene having an intrinsic viscosity corresponding to a molecular weight of 80,000 was dissolved in 49.5 gm. of methyl chloromethyl ether, equivalent to 0.48 mol of polystyrene per 0.64 mol of the ether. To the solution was then added 0.86 g. of zinc chloride. The clear yellow solution was stirred for minutes at room temperature, and slowly turned clear red as the zinc chloride dissolved. The temperature was then slowly raised to 52 C. with constant stirring over a period of 2 /2 hours, at which time the solution was a viscous red syrup. The solution was cooled, stirred for 17 hours, and 12 g. of Water and 4 g. of dioxane added to stop the reaction.

The chloromethylated polystyrene was precipitated by pouring the syrup into excess anhydrous methanol. To insure complete removal of the zinc chloride, the precipitate was redissolved in dioxane and reprecipitated by spraying into water. The product was washed with water, then with methanol, and dried at 50 C. The product was a linear carbon chain polymer containing the regularly recurring linkage l CHzCH-C E;CH2C1 Example 2 A diflerent method for forming a polymeric intermediate suitable for quaternization is illustrated by the following.

A mixture of 20.0 g. (0.92 mol) of a polystyrene having an intrinsic viscosity corresponding to a molecular weight of 80,000, 8.8 g. of paraforrnaldehyde (0.292 mol), 8.8 g. of zinc chloride and 250 ml. of carbon tetrachloride was heated to 74 C. in a flask provided with a reflux condenser. HCl was bubbled through the reaction mixture for about an hour. The product was cooled and poured into an excess of methanol, precipitating a white mass. This mass was washed thoroughly with water, then with methanol, dried at 35 C., and ground to about 20 mesh. The product contained 12.1% chlorine, corresponding to about one chloromethyl group for each four linear carbon chain atoms.

Example 3 A still further method of preparing an intermediate suitable for quaternization is illustrated by the following.

20 g. of polymerized commercial o-,p-dimethylstyrene (0.152 mol) having a molecular weight of about 60,000 was dissolved in 180 g. of carbon tetrachloride in a 500 ml. round-bottomed quartz flask fitted with gas inlet tube and connected to a trap of liquid chlorine. The chlorine was slowly vaporized and allowed to bubble through the solution at about room temperature while the solution was irradiated with ultra-violet light. At the end of two hours, when 40 ml. of chlorine had been bubbled through, the large mass of polymer which had formed was poured into an excess of methanol and the resulting slurry filtered. The residue was washed thorcolloidal cationic dispersion thereon.

8 oughly with water, then with methanol, and finally dried in an oven at 35 C. for three hours. The product contained the recurring linkage A method of preparing a dry strength resin by quaternization of -a pre-formed linear carbon chain polymer carrying chloromethyl groups is illustrated by the following.

10.0 g. (0.066 mol) of a chloromethylated polystyrene corresponding to that of Example 1 was dissolved in 190 g. of dioxane. To this was added 18.0 g. of a 25% aqueous solution of trimethylamine (0.075 mol). A mass of polymer immediately precipitated. With continued stirring, the polymer redissolved to form a hazy yellow solution. After stirring for an hour at room temperature, the polymer began to reprecipitate. Stirring was continued for 12 hours, 300 ml. of water added, and the viscous syrup was concentrated at reduced pressure. The resinous product was dried at 50 C. It analyzed 3.5% nitrogen, and 7.4% chlorine. The product, which contained recurring linkages of the theoretical formula CH1-CH- Cl CHz uCHsh was easily dispersed in warm water, and formed a hazy Analysis showed that it contained about 17 quaternary ammonium groups per linear chain carbon atoms.

Addition of 5% of this polymer, based on the weight of the fibers, as a 1.5% aqueous solution to a slurry of cellulose fibers at 2.38% consistency yielded a paper having a dry strength of 27.0 lb. per inch and a wet strength of 3.6 lb. The same paper which contained none of the resin had a dry strength of 23.0 lb. and a wet strength of 0.4 lb.

Example 5 An "alternative method of solvent removal and addition of water in the preparation of the dry strength resin is illustrated by the following.

The process of Example 4 was repeated up to the point where the dioxane product was concentrated at reduced pressure. The dioxane was stripped from the product by distilling at reduced pressure and water was added to maintain the volume of the liquid constant. An aqueous colloidal cationic dispersion was obtained having a solids content of 5.3% which corresponded to the product of Example 4.

Example 6 A method of preparing a suitable dry strength resin by homopolymerization of a quaternizable monomer followed by reaction of the resulting polymer with an aralkyl chloride is illustrated by the following.

To a flask fitted with thermometer, dropping funnel and reflux condenser and stirrer was added 10.0 g. of p-(dimethylamino)-styrene and 0.20 g. of azo-bis-isobutyronitrile as catalyst. The solution was heated on a steam bath and at the end of two hours the viscous solution was treated with 0.10 g. more of azo-bis-isobutyronitrile and heated for an additional two hours, forming p-dimethylamino-styrene polymer. The semi-solid polymer was dissolved in 40 g. of benzene, reprecipitated in 250 g. of methanol, recovered by filtration, washed with methanol, and dried for 4 hours at 70 C. The cream-colored product Weighed 6.6 g.

2.5 g. of the above-described polymer was dissolved in 25 ml. of benzene and 6.4 g. of benzyl chloride (200% excess) added thereto. The mixture was allowed to stand at room temperature for 64 hours, at the end of which time a precipitate of polymerized benzyl dimethyl vinylphenyl ammonium chloride had formed. The product was collected on a Buchner funnel, washed with 100 ml. of benzene and dried under vacuum. The dry tan polymer weighed 3.8 g. and contained recurring linkages of the theoretical formula The above polymer was dissolved in water to form a colloidal cationic dispersion containing solids.

. Example 7 A 2.5 g. sample of the reprecipitated methanol-washed para-(dimethylamino) styrene polymer prepared in Example 6 was dissolved in ml. of benzene. 6.2 g. of allyl bromide (200% excess) was then added. The solution was maintained at room temperature. Quaternization was complete within about 1 hour. The product was a precipitate which was collected on a Buchner funnel, washed with 100 m1. of benzene and dried under vacuum. The dry tan polymer weighed 4.5 g. When dissolved in water at 1% solids the polymer formed a hazy colloidal cationic dispersion, and contained recurring linkages of the theoretical formula CH2-CH Br CHzIL'(CHa):(CHr-CH=CH2) Example 8 The preparation of a dry strength resin by copolymerization of a preformed monomeric a,fi-unsaturated quaternary ammonium compound with mil-unsaturated compounds is illustrated by the following.

(3-acrylamidopropyl) benzyl dimethyl ammonium chloride was prepared as follows.

Into 624 g. of N-[3-(dimethylamino)propyl] acrylamide, in 1100 ml. of benzene in a round-bottomed flask fitted with stirrer, thermometer, and reflux condenser was slowly stirred 506 g. of benzyl chloride. The temperature was held at 50 C. by an ice-water bath. The reaction mass set to a thick paste, which was cooled to room temperature, was washed with benzene and airdried. The product was dissolved in 1500 ml. of water and the benzene layer removed in a separatory funnel. The'aqueous solution was treated with activated charcoal and filtered, and then diluted to solids with water and adjusted to pH 8.7 with HCl. Titration indicated that the quaternization was 85% complete.

The product was copolymerized as follows. Into a three-necked, round-bottomed flask fitted with reflux condenser, thermometer, stirrer and dropping funnel and provided with an electric mantle heater were charged 28.0 g. of monomeric acrylamide, 8.0 g. of monomeric ethyl acrylate, 13.3 g. of the 30% aqueous solution containing the aforementioned (3-acrylamidopropyl) benzyl dimethyl ammonium chloride and 350.6 g. of water. The reagents were stirred and the pH was adjusted to 6.5 with NaOH. 0.1 g. of powdered ammonium persulfate was then added. The turbid solution was heated to 80 C. and maintained at this temperature for about 4 hours, after which the clear syrup which formed was cooled to room temperature. The pH was again-adjusted to 7.5 -with. sodium I 10 hydroxide. The product which contained the-recurring groups w CH2CH UHF-(3H o o=0 NHz CaHs and CHI-CH- =0 i 01 NH (omhmomh was a viscous water-soluble cationic syrup.

(3-acrylamidopropyl) benzyl dimethyl ammonium chloride and methods for the preparation thereof are disclosed and claimed in co pending application Serial No. 286,003, filed May 3, 1952, by John A. Price. The application discloses further quaternary ammonium salts which are advantageously used in the process of the present invention, and these samples are incorporated in the present specification by reference.

Example 9 3-[bis(2-hydroxyethyl)] amino propylamine,

(H0CH CH N CH NH was reacted with potassium cyanate and to form 3-[-b1s (2-hydroxyethyl)] aminopropylurea HO CH2CH2N(CH2)sNHfiJ-NH:

41.0 (0.2 mol) of the product was dissolved in water and 23.1 g. (0.25 mol) of epichlorohydrin added. The mixture was heated at 60 C. for 24 hours. 4 g. of the aqueous solution containing about 50% by weight of ureidopropyl bis(2 hydroxyethyDglycidyl ammonium chloride of the theoretical formula CHzCHCHz [H O (0 H2) 2]2N( CH2) :NH (ll-NH:

was added to 10 g. of 37% formaldehyde. The mixture was added to 71 g. of a 10% aqueous polyacrylamide solution. The resulting solution was acidified to pH 6.0, heated to F. for 30 minutes, and then diluted to a solids content of 7.5% by weight. The product was an aqueous dispersion of a linear polymer in cationic form which, when further diluted with water, exhibited a bluish colloidal haze. It contained recurring linkages of the theoretical formula wherein R is GHaCHCHz [H0(omhhNwmhNflc Nn I j FY;- or a hydrolysis product thereofi.

cationic linear polymer was obtained, whichalso exhibtited, ton dilution, .a :bluish "colloidal :haze.

or a hydrolysis product thereof.

Example 11 S-(dimethylamino)propionamide was quaternized by the use-of methyl iodide. 25.8 g. (0.1 mol) of the prodnot,

(CH3)3N(CH1)2C NHz was reacted with 8.1 g. (0.1 mol) of 37% formaldehyde. The product was added to a aqueous solution containing'71 g. (1 mol) of polymerized acrylamide and the mixture adjusted to pH 6. The mixture was heated to about 185 F. for 45 minutes and cooled to room temperature. The product was a somewhat viscous solution which, when diluted, exhibited a colloidal haze. It

contained recurring linkages of the theoretical formula Example 12 To g. of hide glue dispersed in 180 g. of hot water was added 10 g. of a 50% solution of ureidopropyl-bis- (Z-hydroxyethyl) glycidyl ammonium chloride. The mixture was heated at 60 C. for 24 hours. The product was a linear protein polypeptide containing recurring linkages of the theoretical structure I OH NH Example 13 A mixture of 180 g. of benzene, 108 g. of vinyl acetate, 12 g. of 2-morpholinylethyl vinyl ether, and 0.1 g. of azobisisobutyronitrile was refluxed for 3 hours in a 1- liter, 3-neck flask equipped with a condenser, thermometer and stirrer. The uncombined monomers and the henzene were removed by steam distillation and the product was oven-dried at 70 C. The yield was 31.5 g.

25 g. of the product described above was dissolved and 225 g. of methyl alcohol and a solution of 0.2 g. of sodium metal and 25 ml. of methyl alcohol was added. The mixture was heated with stirring under reflux. After about 5 minutes solid polymer began to separate. After minutes reflux the slurry was filtered, washed with methyl alcohol and dried at 70 C. The yield was 14.5 g. Analysis showed 0.87% nitrogen. 10 g. of the alcoholysis product dissolved in g. of water was treated with 5 g. rofallyl bromide under reflux 'for 1 /2 hours, and'then was allowed to stand at room temperature for 13 .days. The brown viscous solution was found by titraition for .ionic bromide to be substantially completely :quaternized. It "containedjrecurring linkages of the theoretical formula -OH1-'CHCH;CH

H Br

( 1 Ha CH:N

Example 14 CHa-CH:

Into a 3-neck, 'l-liter flask equipped with thermometer, condenser and stirrer was charged 32 g. of acrylamide, 4 g. of the (3-acrylamidopropyl)benzyl dimethyl ammonium chloride of Example 9,4 g. of acrylic acid, and 12 g. of isopropyl alcohol, 348 g. of water, and 0.1 g. of ammonium persulfate. The mixture was heated for six hours at C. The product was a clear viscous syrup which .was miscible with water. It contained about 12 quaternary ammonium groups per 1000 linear chain carbon atoms.

Example 15 230 g. of N,N-dimethyl-p,p-methylenebisanilane (1 mol) and 500 -g. of t-butanol containing a trace of sodium hydroxide are placed in around-bottomed flask equipped with thermometer, stirrer and reflux condenser. Ethylene oxide is bubbled through until six mols have been adsorbed, and 202 gm. (1 mol) of 1,3-dibromopropane is added. The mixture is heated to reflux to initiate the reaction which is then allowed to continue at 80 C. When reaction is 99% complete as found by titration (corresponding to a "calculated molecular weight of 61,600), the alcohol is evaporated, and the product dissolved in water to adjust'the solids content to 10%. A linear polymer is obtained containing recurring linkages of the theoretical formula CH CH3 K! i/ mCHnCHnCHrTOCH 1 0 ,C

A A CH3 CH1 CH2 CH1: 0 O V5 V3 This illustrates a linear polymer in which nitrogen atoms and benzene rings form a part of the chain.

Example 16 The effect of a number-of resins of the presentinvention in producing paper of increased dry strength was determined by forming a :master batch of unbleached northern kraft pulp beatento a-Green freeness of 500 cc. and adjusting the'slurry to a consistency of 0.6%. Aliquots were withdrawn, adjusted to the pH values shown in the table below by addition of hydrochloric acid or sodium hydroxide as required. Certain aliquots were reserved as controls, and to these nothing else was added. T o thelremainder polymer solutions were added as shown in the table, after which the aliquots were stirred and Example 9, the particularreagents employed in eachinstance and the amountsthereof being shown in the table. Results are as follows:

of the stock being-"45. The strengthening'agents-contained combined formaldehyde, and was formed by co- Polymer Reagents (Parts by Weight) Tensile Strength 4 StookpH Basis, Dry Acryl- Methyl Acrylo- Ethyl Wt. Lb. Wet- Test No; Quat. amide Acryb Nltrile Acrylate Found amide Found Percent w Increase 44.9 21.7 t 0.6 90 4.5 45.9 30.3 39.6 3.7 90 9.0 46.2 30.2 39.2. 2.3 85 4.5 50.2 28.9 32.7 3.1 85 9.0 48.0 30.4 39.9 1.6 80 4.5 45.9 29,4 36.5 p 2.4 v 80 9.0 46.9 -29.4 36.5 1.4 44.1 -;24.2 I v 0.7 95 -45 44.5 32.0 32.2 4.9 -Q 05 9.0 43.6 33.3 37.6 2.9 95 4.5 42.8 33.8 39.8 1.2 95 9.0 44.1 38.3 58.0 3.6 51.1 25.2 L 0.5

90 4.5 50.8 32.5. 29.0 t 2.7. 90 9.0 50.5 38.2 51.5 as 70 4.5 49.7 30.3 20.2 2.4 7 9.0- 48.2 [33.2 -'31. 7 2.8

1 3-(Acrylamidopropyl) benzyl dimethyl ammonium chloride.

1 in 407600. 8 Corrected to 50 lb. basis weight. 1

The test sheets were indistinguishable in appearance and feel from the control sheets. M

The manufacture of high dry strength, well-sized paper is illustrated by the following, I

- The paper-forming process of the--previous example was followed with two exceptions. I

(*1) The fibers were sized by the addition of 3% liquid gum rosin size (solids based on the dry weight of the fibers) followed by the addition of 4% of alum, and

(2) The sheets were prepared in duplicate, one set of sheets being dried at room temperature (75 -F.), the

other set being dried at the normal temperature of The strengthening agent employed was formed by copolymerizing' 90 parts by weight of acrylamide with 10 parts by weight of 3-(acrylamidopropyl)benzyl dimethyl ammonium chloride by the method of Example 9 to a molecular weight as estimated from viscosity measurement of about 150,000. Three percent of the strengtl1ening agent based on the dry weight of the fibers was added in each case except the controls, which therefiore contained only rosin size and alum.

polymerizing 5 partsbyweight of B-(acrylamidopropyl) benzyl dimethyl ammonium chloride with 95 parts by weight of N-hydroxymethylacrylamide (prepared from acrylamide and formaldehyde); v3%'- of the resin was added based on the dry weight of the fibers. The paper was dried for 10 minutes atr260 F., and the results are shown in comparison with one control which contained no polymer and a second. control which was dried at 1 Sheets 25" x 40" 600. 2 Lb./in. correete to 451b. basis weight.

We claim: 1. Dry paper of improved dry strength composed of Results are as follows: water-laid cellulose fibers bonded together by an irre- Tensile Strength Rosin Cop0ly Drying Currier Run Added, mcr Basis Temp., Dry 'Iest Percent Added, Wt. Lb. F. Wet- (Secs.) Percent Fonnd Found 5 Percent Increase 3 Nil 45.3 75 19. 0.9 34 3 3 47. 4 75 31. 50. 6 2. 1 36 3 Nil 42.8 240 21.2 1.5 52 3 3 42. 1 240 33. 0 55. 5 4. 7 50 l Solids based on dry weight of the fibers. 1 25' 1: 407500. 3 Corrected to 45 lb. basis weight.

This test shows that the strengthening agents of the versibly and uniformly adsorbed content of between about present invention are compatible with rosin size, and that 0.01% and 5% of their weight of a normally hydrophilic very satisfactory dry strength paper can be made there- Water-soluble cationic linear polyalkane chain polymer with. The results show that the eifect of the application having an average molecular weight of at least about of heat during drying on the strength of the paper is to 10,000 and containing quaternary ammonium groups. decrease the dry strength and to increase the wet strength. 2. Paper according to claim 1 wherein the polymer Example 18 A paper of both high wet strength and high dry strength was prepared from unbleached northern kraft pulp according to the procedure of Example 16, the pH has an average molecular weight between about 50,000 and 200,000.

3. Paper according to claim 1 wherein the weight of polymer is between about 1% and 3% of the weight of the fibers.

15 -4. Paper according to claim -1 wherein the polymer contains'the recurringgroups CHa-CH =0 CzHs and CHPCH l-=0 NH )sN( H-:)=

cHzCe a 5. Dry paper of improved dry strength composed of water-laid cellulose fibers bonded together by an irreversibly and uniformly adsorbed content of between about 0.1% and 5% of their weight of a normally hydrophilic water-soluble cationic linear polyalkane chain polymer having an average molecular weight of at least about 25 ,000 and containing between about 1 and 15 quaternary ammonium groups for each 1000 linear chain atoms.

6. Filled dry paper ofimproved dry strength composed of water-laid cellulose fibers bonded together by an irreversibly and uniformly adsorbed content of between about 0.1% and 5% of their weight of a normally hydrophilic water-soluble cationic linear polyalkane chain polymer having an average molecular weight of at least about 25,000 and containing quaternary ammonium groups, said paper having a uniformly distributed content of from 2% to 30% of'a carbonatefiller.

7. Paper according to claim :6 wherein the filler is calcium carbonate.

8. Sized 'dry paper of improved zstrength composed of rosin-sized water-laid cellulose zfibers "bonded :together by an irreversibly and uniformly adsorbed content of between about 0.1% and 5% of their weight of a normally hydrophilic water-soluble cationic linear polyalkane chain polymer having an average molecular weight of at least about 25,000 and containing quaternary ammonium groups.

9. A method of manufacturing paper of improved .16 dry strength which consists essentially in forming an aqueous suspension of paper-making cellulosic fibers, mixing therewith from 0.01% to 5% of their weight of a hydrophilic water-soluble cationic linear polyalkane chain polymer having a molecular weight of at least 10,000 and containing quaternary ammonium groups whereby said polymer is irreversibly and uniformly ad- 'sorbed by said'fibers, and sheeting'and drying said fibers,

References Cited in the file of this patent UNITED STATES PATENTS 2,067,234 Gordon Jan. 12,1937 2,338,602 Schur Jan. 4, 1944 2,345,543 Wohnsiedler et al. Mar. 28, 1944 2,454,547 Bock Nov. 23, 1948 2,595,225 Coffman 'May 6, 1952 2,595,935 Daniel et a1. May 6, 1952 2,601,597 Daniel et al June 24, 1952 2,654,729 Price Oct. 6, 1953 2,676,166 Webers Apr. 20, 1954 2,677,679 Barney May 4, 1954 2,698,793 Landes Jan. 4, 1955 2,745,744 Weidner May 15, 1956 2,765,229 McLaughlin Oct. 2, 1956 FOREIGN PATENTS 714,585 Germany Dec. 3, 1941 884,560 France Apr. 27, 1943 124,900 Australia June 22, 1945 154,799 Australia Apr. 26, 1951 

